A comparative study of silver electrodeposition from pyrophosphate-cyanide and high concentration cyanide electrolytes in the presence of brighteners

Abstract

A study of the electrodeposition of silver from 2 different types of electrolytes; (1) neutral pyrophosphatecyanide electrolyte and (2) alkaline high concentrated cyanide electrolyte in the presence of a variety of additives suchas 2-mercaptobenzothiazole, potassium selenocyanate, and potassium antimony tartrate was performed. Influenceof additives and cyanide concentration on microstructure and kinetics of the cathodic processes were studied. Abrightener couple, 2-mercaptobenzothiazole and potassium antimony tartrate, were combined within this investigationand detected to be highly effective for silver electrodeposition. The rapid increase in current density at the same potentialinterval related to grain refinement effect of potassium antimony tartrate was shown. The cyclic organic compound, 2-mercaptobenzothiazole, polarizes the reduction to high cathodic potential in pyrophosphate electrolyte. However, thesufficient levelling effect required for the mirror-bright appearance seems to be related to the high polarizing effect of thehigh concentration cyanide content. In the case of pyrophosphate electrolytes, sufficient levelling cannot be achieved,so semigloss coatings are obtained. The low cathodic potential electrodeposition of silver in pyrophosphate electrolyte,which is found to proceed by 3D instantaneous nucleation, is polarized to high cathodic potentials and grows into 3Dprogressive nucleation and diffusion-controlled growth in high concentration cyanide electrolyte.